Crew was reduced from six to five. The mission design featured increased commonality to reduce the number of new spacecraft to be developed; redundancy to improve mission safety; a heavy-lift launch vehicle family based on newer Delta-IV technology; improved trajectories; no more than one earth-orbit rendezvous; and no nuclear rocket development (although nuclear power on the Martian surface was still proposed).

In 1999 the Mars Society, noting certain defects in NASA's Design Reference Mission, requested California Institute of Technology to develop an alternative scenario to meet these concerns. Crew was reduced from six to five. The mission design featured increased commonality to reduce the number of new spacecraft to be developed; redundancy to improve mission safety; a heavy-lift launch vehicle family based on newer Delta-IV technology; improved trajectories; no more than one earth-orbit rendezvous; and no nuclear rocket development (although nuclear power on the Martian surface was still proposed).
The Mars Society Mission featured:

Increased commonality of design for reduced development.

Increased redundancy for maximum safety. A Crew Return Vehicle would accompany the outbound habitat module, and in the event of habitat failure would be able to support the crew until arrival on Mars or Earth. After a 612-day surface stay, both the Mars Ascent Vehicle (MAV) and Earth Return Vehicle (ERV) would accompany the crew during the return to Earth. If either ERV or MAV failed, or Mars orbital rendezvous did not take place, either component could return the crew.

A modular family of launch vehicles was proposed. This Qahira Interplanetary Transportation System (QITS) would use the latest proven Delta IV EELV lower-cost expendable technology. The heavy lifter version would use only two new components, the Qahira Booster Core (QBC) with 4 RS-68 engines, and the Qahira Upper Stage (QUS), with 1 RD-0120 engine. The maximum configuration, the Q3041, would be capable of sending 55 metric tons on a trans-Mars trajectory.

Detailed and improved trajectories were developed, including a 3/2 Hohmann transfer orbit for the ERV that minimized propellant boil-off and reduced launch facility strain, as well as optimal trajectories for cargo, free-return, and return from Mars surface.

Minimal assembly in Earth orbit, specifically no more than one Earth orbit rendezvous.

No nuclear thermal rocketry, and no activation of nuclear power sources until Mars surface.

A large science payload, with 13.7 metric tons available for the 2014 mission.

The mission profile was as follows:

On July 1, 2011 a Q3041 Launch Vehicle would send an Earth Return Vehicle on a low energy trans-Mars trajectory. The Earth Return Vehicle consisted of a Crew Return Vehicle and a methane-oxygen rocket stage. A second Q3041 launch on October 27, 2011 would send to Mars a cargo vehicle with surface mobility containing liquid hydrogen feedstock, a 160-kWe nuclear reactor, and science equipment. A third Q3041 would launch the Mars Ascent Vehicle (MAV) on November 11, 2011. The MAV consisted of a CRV and methane-oxygen rocket stage, identical to that on the ERV, with attached first stage and ISRU unit.

On August 24, 2012, the cargo payload would aerobrake into Mars orbit. After verifying the landing site for the base on Mars, it would aerobrake again to reach the Martian surface. It would deploy the nuclear reactor, and place a radio beacon at a site to allow precision landing nearby of the other base elements. The MAV would join the landed cargo on September 7, 2012. The ISRU unit aboard the MAV would activate and be connected to the nuclear reactor and hydrogen feedstock, and began making rocket propellant and life support oxygen (methane and oxygen) for the crew to return later.

The Earth Return Vehicle would aerobrake into an elliptical Mars orbit with a three-Martian-day period on July 15, 2013.

On November 20, 2013, a second MAV intended for the 2016 follow-on mission and including a large science payload would depart Earth on a Q3041, followed by a Q3041 cargo launch containing liquid hydrogen for the 2016 mission and the pressurized rover to be used by both the 2014 and 2016 missions.

By early January 2014, the ISRU unit's propellant manufacture on the surface would be complete and it would detach to be used for future MAV's. Verification that the ISRU had succeeded would be followed by the launch to low-Earth orbit of an unmanned habitat module aboard a Q3041. The crew would launches in a Crew Return Vehicle on a smaller Q1310 and dock with the habitat spacecraft in low earth orbit. On January 11, the upper stages of first the Q1310 and then the Q3041 would accelerate the crew, CRV, and habitat module into a 134 day trans-Mars trajectory. During the coast to Mars a 125-m truss would deploy and the CRV and habitat module would be spun to provide artificial gravity for the crew.

On May 25, 2014, the habitat and CRV would reach Mars. The uncrewed CRV would fly by Mars and return to Earth on a free return trajectory for reuse. The habitat with the crew would aerobrake into Mars orbit, and then land on the surface. They would be followed by the 2016 mission cargo payload on July 4 and the 2016/backup MAV on September 15.

The crew spends 19 months exploring the Martian surface.

In January 2016, the crew boards the MAV, which launches them to rendezvous with the ERV parked in Mars orbit. On January 27, firing first the ERV's and then the MAV's engines, both ERV and MAV accompany the crew back to Earth.

While the first crew was coasting back to earth, the second 2016 crew was launched toward Mars. On December 25, 2015, the CRV that escorted the 2014 Mission returns on its free return trajectory from Mars and aerobrakes into a parking orbit. The 2016 crew and habitat were launched separately. After a series of maneuvers and dockings, the 2016 second crew depart for Mars aboard the 2014 CRV and a new habitat module.

As in NASA scenarios, the build-up and resupply of the base then continues. The lower crew size and improved mission scenario allowed the MSM component masses to be reduced by 10% from NASA's DRM 3.0: